1. Field of the Invention
The subject invention relates to display devices, and in particular, to projection television receivers.
2. Description of the Related Art
Projection television receivers enable the formation of large displays economically. These projection television receivers typically include three projection tubes formed by cathode ray tubes which are arranged in a horizontal plane. The images from these projection tubes are then focused to form a single image on a display screen. Typically, the center one of these three projection tubes is in registry with the screen. However, the outer two tubes form trapezoidal images on the display screen which need to be corrected such that they are in convergence with the image from the center projection tube. Furthermore, even the image from the center tube may not form a correct geometry image and, as such, needs to be corrected.
To this end, projection television receivers include convergence correction circuits in which the horizontal and vertical deflection signals to each of the three projection tubes are adjusted such that convergence and geometry errors are corrected. The adjustment of these circuits is tedious and involves an operator determining, by eye, whether the adjustments are proper.
It is an object of the present invention to provide a method and an apparatus that electronically re-maps the pixels in a video signal such that convergence and geometry errors are compensated.
It is a further object of the present invention to provide a method and an apparatus that corrects for convergence and geometry errors without, or in addition to, modifying the horizontal and vertical scanning signals.
The above objects are achieved in an apparatus for correcting convergence and geometry errors in display devices comprising an input for receiving a digital video signal; means for determining intended horizontal and a vertical addresses for each pixel in said video signal; means for generating actual addresses for each pixel corresponding to an actual horizontal and vertical location in a displayed image, said actual horizontal and vertical location being based on a particular display device; and means coupled to said input, said determining means and said generating means for storing the pixels in the digital video signal and for outputting said pixels at an appropriate time whereby errors between said intended and actual addresses are corrected.
The subject invention recognizes that certain convergence and geometry errors are inherent in, for example, projection television receivers and are repeatable unless corrected. By measuring and storing these errors, the positioning of the pixels in a video signal, i.e., the time when each pixel is outputted, may be adjusted such that in the resulting image, these errors are compensated. The apparatus applies geometric pre-distortion to a digital video signal in order to compensate for distortion in the display device.